Many adhesives including hot melt adhesives are useful for bonding various substrates together such as wood, paper, plastics, and textiles, as well as other materials. One use for which hot melt adhesives are well suited is the fabrication of corrugated paper board. Hot melt adhesives, useful for producing corrugated paper board, must have high bond strength under conditions of shock, stress, high humidity, and extremes of temperature encountered in transportation and storage. In addition, the melt point, wetting time, initial tack, setting time, pot life, and general handling qualities on automatic corrugated board machinery are essential considerations.
At present, it is very desirable to recycle paper, paper products, and other disposable products to conserve material resources and to avoid large additions to landfill space. It is thus a general practice in the paper industry to recover the used and waste corrugated material and repulp the material for use in the preparation of other materials such as cardboard. The use of polyolefin hot melt adhesives to close or seal cartons made from corrugated material has presented problems in regard to repulpability of the used boxes or cartons (see U.S. Pat. Nos. 4,070,316; 4,127,619; 4,146,521; 4,460,728; 4,471,086; and 4,886,853). In fact, all the presently available hot melt and pressure sensitive adhesives are largely water insoluble and very difficult to disperse during the repulping process. This fact makes certain paper products, in which adhesives are necessarily utilized, unattractive since failure to disperse the insoluble adhesives results in lower quality recycled paper having variable composition and nonuniformity and thus, lower product value.
One approach to avoid the presence of insoluble adhesives in the recycled paper products is to use adhesives whose density is different from the density of water and pulp in water, thus permitting gravitational separation. However, this requires separation steps which can increase the recycling costs of the paper products containing adhesives.
Another approach could be to use a water soluble adhesive that would be separated from the pulp and dispersed into the water during repulping. This type of adhesive would remain in the water when the pulp is recovered. However, presently available water soluble or dispersible adhesives are "natural" adhesives such as dextrins, cellulose gums, and animal glues derived from the hides and bones of animals and these adhesives have lower strength, fail to adhere well to paper and wood stocks with coatings or heavy ink applications, and sometimes require special treatment and handling because of their high viscosity. Therefore, the use of these adhesives, while being easily recyclable, is quite low due to poor adhesive characteristics. Attempts to produce synthetic water-dispersible hot melt adhesive compositions have heretofore been unsuccessful due to resulting poor adhesive properties such as thermal stability, low strength, poor viscosities and low cold flow resistance. Additionally, costs and ease in manufacturing have precluded their use (see U.S. Pat. Nos. 3,919,176 and 5,098,962).
In addition to paper and paper products, there are many disposable products, such as diapers, in which hot melt adhesives are used. The use of current hot melt adhesives in these products complicate attempts to recycle products and separate out the insoluble sticky hot melt adhesives.
In light of the above, it would be very desirable to produce a water-dispersible adhesive, particularly a hot melt adhesive, at reasonable costs that maintains the desirable properties of presently available adhesives.